1. Field of the Invention
The present invention concerns improvement to steerable wheels of land vehicles the suspension of which is ensured through two lateral arms located on a single side of the wheel.
Such devices are known in the prior art and in particular in French Patent published under No. 2 418 141. According to this patent, the front suspension has the general form of a quadrilateral of which the apices are the ends of two arms, pivoted on one of their ends on an element integral with the body of the vehicle and at the other end on a stub axle bracket triangle of the front wheel.
The axle corresponding to the side of the said stub axle or swivel pin triangle associating the ends of the arms allows to turn the front wheel. It is materialized by two hinging and pivoting devices with the ends of the arms, of the ball and socket type or equivalent. The two arms are mounted in rotation on the vehicle body due to two substantially horizontal axles (in normal positioning of the vehicle) and they are situated substantially in a single vertical plane thus containing the centres of the ball and socket joints and the turning steering axis passing through these centers.
The shock absorbing and suspension system per se is essentially constituted by a spring shock absorber assembly generally disposed between an arm and an element integral with the vehicle body. When the suspension is actuated, the arms pivot in the said vertical plane, provoking the displacement in this single plane of the swivel type joints and thus the turning steering axis.
With respect to the steering system itself, it is constituted by a side lever integral with the triangle moved by a transmission transmitting to the said lever the movements of the handlebar or other steering control device.
However, the major difficulty encountered in producing this steering assembly is to allow the suspension to function without introducing any stray variation of the steering angle defined itself by the handlebar or equivalent.
In fact, if for example the handlebar imposes upon the vehicle straight driving, when the suspension functions, the end of the lever integral with the triangle must follow a curve in a plane parallel to the vertical plane of the arms. If the kinematic steering control transmission is not adapted to allow the end of the lever to follow this curve, the foreseen steering angle is not respected and, for example, oscillations of the suspension can provoke oscillations of the steering angle with the consequences that this involves on the driving of the vehicle.
The problem has been solved in the case of parallel arms of the same length and thus of the parallelogram quadrilateral since the movement of any point associated to the stub axle bracket is thus a pure rotation of which the radius is equal to the length of the arms.
In this case, it is sufficient that the kinematic transmission presents a bar the length of which is that of the arms, which is pivotally connected to the said lever at one end and the other end of which pivots around a point located adjacent to the opposite side of the parallelogram. Preferably, this bar is displaced substantially parallel to the vertical plane of the arms when for a given steering angle the suspension functions.
But, in the case of non parallel arms and/or arms of different lengths, the solutions are difficult to find and only remain approximate once each point associated to the triangle follows a complex curve.
The object of the present invention is to provide a solution as precise as possible to this problem while allowing the suspension to perform its function whatever the turning or steering angle defined by the handlebar or equivalent, and without bringing to the steering angle any stray variation.
In the description given herein-above, reference will be made to motorcycles that represent a typical application example of suspensions having two lateral arms, it being well understood that it concerns a non-limitative example and that the invention can apply to all vehicles presenting at least one front wheel mounted on two arms adapted to pivot and/or oscillate around substantially horizontal axes (in the normal position of the vehicle). In the case of the motorcycle, and in particular of the motorcycle with two wheels, will be called the axial plane of symmetry, the longitudinal plane with respect to which most of the constitutive elements are symmetrical and especially, body, saddle, rear wheel, and, when the steering angle is nil, front wheel and handlebar.
When the motorcycle is riding straight, this plane is substantially vertical and the wheel axles are substantially horizontal. In the following description, and in order to simplify the wording, the references to the verticality and the horizontality will correspond in the case of the vertical symmetry plane, it being well understood that in the case of cornering or banking the assembly inclines normally from the side of the center of the curve followed.
Furthermore, when the suspension is fixed in a given position, it is necessary that the steering control be transmitted from the handlebar or equivalent to the stub axle; the linearity of the transmission of the steering angle being necessary so that the driver can regularly adjust the steering angle. If this condition is satisfied, as well as the preceding one on the keeping of a given steering angle when the suspension functions, it is thus possible to cause to act without disturbances simultaneously the steering control and the suspension.